Mid Sweden University

Lightweight materials with high strength are desirable for advanced applications in transportation, sports equipment, construction, automotive, and aerospace. Aspen is fast growing, has low flammability, and is renewable and readily available. In this study, we present a continuous, high-yielding, efficient, scalable, and sustainable approach for the fabrication of strong materials from aspen by synergistic selective chemical modification and continuous hot pressing. FTIR analysis revealed changes in the chemical composition of the wood polymers, including the introduction of anionic groups, while SEM images showed morphological and structural transformations such as smoother surfaces and a more compact wood structure. The proposed strategy achieved up to 258 MPa (530% increase) in tensile strength by combining enhanced ion-bonding and hydrogen-bonding with the alignment of cellulose nanofibrils and the solidification of softened, depolymerized lignin through cross-linking reactions. This work demonstrates the continuous large-scale production of lightweight, strong structural materials under energy-efficient and mild modification conditions, suitable for the green fabrication of next-generation advanced materials from wood. 

Sodium thiopental (STL) is an ultrashort-acting barbiturate that acts quickly on the brain, reduces levels of adrenaline, noradrenaline, and dopamine, and has neuroprotective properties. However, its side effects, especially in high doses, can be severe, including respiratory failure and cardiac complications. Molecularly imprinted polymers (MIPs) are three-dimensional polymeric networks that mimic the structure and functionality of target molecules. MIPs include benefits such as stability, selectivity, and cost-effectiveness. Combination with magnetic nanoparticles (MNPs) not only enhances their stability and biocompatibility but also provides magnetic separation capabilities. This research introduces the design and synthesis of pH-sensitive MIPs as targeted nanocarriers for the selective uptake and controlled release of STL molecules. The MIPs were synthesized in various forms, including magnetic core MIPs (MMIPs), standard MIPs (MIPs), and fiber-shaped MIPs (MIPF), to explore their comparative efficiency and structural advantages. Bemegride (BMG), an antidote structurally similar to STL, was utilized to evaluate the selectivity of these MIP systems. The formation of specific binding sites of STL on MIPs during the polymerization process leads to selective recognition and matches STL's shape, size, and functional groups. In this regard, all types of MIPs exhibited significant rebinding affinities over their non-imprinted polymer (NIP); specifically, MMIPs displayed a high affinity for uptake of STL (393.8 +/- 1.328%) against BMG (360.72 +/- 6.72%) over 24 h. The pH sensitivity of the nanocarriers was investigated in simulated gastric fluid (SGF) and simulated intestinal fluids (SIF) environments. The quantitative results indicated that the prepared nanocarriers showed a controlled release in SIF environments. MMIPs achieved a release efficiency for STL and BMG of approximately 57.7 +/- 0.6% and 85.4 +/- 4.6%, respectively, over a 78-hour period. These findings highlight the potential of MMIPs for dual-uptake and targeted release applications of STL in specific pH environments.

Highly selective conjugate additions of Grignard reagents to cyclic and linear enones catalyzed by recyclable heterogeneous polysaccharide/nanocopper catalysts are disclosed. The method also allows the synthesis of ketones with an all-carbon quaternary center. When integrated with catalytic asymmetric tandem reactions using enals and β-ketoesters, it yields chiral β,δ-disubstituted ketones with high stereoselectivity. 

Due to challenges such as sustainability and increasing carbon footprint, there is a growing demand to replace fossil-based materials with green sustainable alternatives like cellulosic materials. However, unmodified cellulosic materials often encounter issues like high wettability and low mechanical strength that limit their applicability. To overcome these drawbacks, functionalization and modification are crucial and inevitable. Reported methods often involve toxic/harsh conditions or reagents, and multi-step processes. The focus of this thesis is on the fabrication, functionalization, and modification of cellulosic materials through facile and eco-friendly approaches to enhance their properties and broaden their potential applications.

We started with immobilizing copper nanoparticles on controlled pore glass substrate and used it as a recyclable heterogenous catalyst for the copper-catalyzed alkyne-azide cycloaddition (CuAAC). Focusing on sustainability, we also employed cellulosic materials as catalyst supports. First, cellulose was functionalized using a mild organocatalytic approach. Then, copper or palladium nanoparticles were immobilized onto the functionalized cellulose and used as effective recyclable heterogeneous catalysts in different reactions.

Direct esterification of CNC materials with thioglycolic acid was performed enabling us to introduce thiol groups onto CNC materials. The reaction occurred under mild conditions using natural nontoxic organic acid as an organocatalyst. The method was applied on different CNC materials, producing the corresponding thiol-functionalized CNC materials. The thiol-functionalized CNC was used as a heterogeneous recyclable reducing agent to reduce Cu(II) to Cu(I), which is the active form of copper in CuAAC. The prepared thiol-functionalized CNC materials further functionalized with attaching UV active molecules via thiol-ene click chemistry.

Lactic acid (LA) functionalized CNFs were prepared by using an ecofriendly one-step reaction method in high yields. This was achieved by converting pulp fibers into nanofibrillated cellulose lactate under mild conditions, using LA as both reaction media and catalyst. The process was concurrent and involved an autocatalytic esterification reaction without using metal-based or harsh acid catalysts. Moreover, the LA media were recycled and reused in multiple reaction cycles. 

In the fourth study, strong hydrophobic cellulosic materials were prepared via a facile, scalable and eco-friendly method. The method involves a betulin treatment and hot-pressing processes. First, a water-based betulin formulation was developed and used for the treatment of cellulosic materials. The betulin-treated samples were then hot-pressed. Hot-pressing altered the morphologies and led to dense structures. Moreover, it caused a polymorphic transformation of the betulin particles. Water contact angle and tensile tests revealed that the applied betulin/hot-pressing treatment method noticeably enhanced the samples’ hydrophobicities as well as their tensile strengths. Furthermore, a synergistic effect was noticed between the hot-pressing, betulin treatment, and sulfonation during the pulping process.

Densified and strong large veneers were fabricated via a facile and scalable method. The method involves a combination of chemical modifications of aspen veneers followed by hot-pressing. The study showed that hot-pressing enhanced the tensile strengths. The chemical modifications further improved the efficiency of the hot-pressing, resulting in higher tensile strengths. The chemical modifications changed the wood’s composition promoting wood softening and increasing the bonding. Since the method uses convenient and mild treatments combined with continuous hot-pressing, it enables the processing of large samples. It can also lower time/energy consumption, production costs and the environmental impact.

There is a growing demand for the utilization of sustainable materials, such as cellulose-based alternatives, over fossil-based materials. However, the inherent drawbacks of cellulosic materials, such as extremely low wet strength and resistance to moisture, need significant improvements. Moreover, several of the commercially available wet-strength chemicals and hydrophobic agents for cellulosic material treatment are toxic or fossil-based (e.g., epichlorohydrin and fluorocarbons). Herein, we present an eco-friendly, high-yield, industrially relevant, and scalable method inspired by birch bark for fabricating hydrophobic and strong cellulosic materials. This was accomplished by combining simple surface modification of cellulosic fibers in water using colloidal particles of betulin, an abundant triterpene extracted from birch bark, with sustainable chemical engineering (e.g., lignin modification and hot-pressing). This led to a transformative process that not only altered the morphology of the cellulosic materials into a more dense and compact structure but also made them hydrophobic (contact angles of up to >130°) with the betulin particles undergoing polymorphic transformations from prismatic crystals (betulin III) to orthorhombic whiskers (betulin I). Significant synergistic effects are observed, resulting in a remarkable increase in wet strength (>1400%) of the produced hydrophobic cellulosic materials.

Herein, we describe a solvent-free bioinspired approach for the polymerization of ethylene brassylate. Artificial plant cell walls (APCWs) with an integrated enzyme were fabricated by self-assembly, using microcrystalline cellulose as the main structural component. The resulting APCW catalysts were tested in bulk reactions and reactive extrusion, leading to high monomer conversion and a molar mass of around 4 kDa. In addition, we discovered that APCW catalyzes the formation of large ethylene brassylate macrocycles. The enzymatic stability and efficiency of the APCW were investigated by recycling the catalyst both in bulk and reactive extrusion. The obtained poly(ethylene brassylate) was applied as a biobased and biodegradable hydrophobic paper coating.

Ethylene brassylate is a renewable macrolactone from castor oil that can be polymerized via ring-opening polymerization (ROP) to obtain a fully biosourced biodegradable polyester. ROP mediated by organometallic catalysts leads to high molar mass poly(ethylene brassylate) (PEB). However, the use of metal-free organocatalysis has several advantages, such as the reduction of toxic and expensive metals. In this work, a novel cellulose nanofibril (CNF)/PEB nanocomposite fabrication process by organocatalysis and reactive extrusion (REx) is disclosed. Here, ROP was carried out via solvent-free REx in the presence of CNFs using organic 1,5,7-triazabicyclo[4.4.0]dec-5-ene as a catalyst. Neat or lactate-esterified CNFs (LACNF) were used as initiators to investigate the effect of surface topochemistry on the in situ polymerization and the properties of the nanocomposites. A molar mass of 9 kDa was achieved in the presence of both unmodified and LACNFs with high monomer conversion (>98%) after 30 min reaction in a microcompounder at 130 °C. Tensile analysis showed that both nanofibril types reinforce the matrix and increase its elasticity due to the efficient dispersion obtained through the grafting from polymerization achieved during the REx. Mechanical recycling of the neat polymer and the nanocomposites was proven as a circular solution for the materials’ end-of-life and showed that lactate moieties induced some degradation. 

Celulose nanofibers are lightweight, recycable, biodegradable, and renewable. Hence, there is a great interest of using them instead of fossil-based components in new materials and biocomposites. In this study, we disclose an environmentally benign (green) one-step reaction approach to fabricate lactic acid ester functionalized cellulose nanofibrils from wood-derived pulp fibers in high yields. This was accomplished by converting wood-derived pulp fibers to nanofibrillated “cellulose lactate” under mild conditions using lactic acid as both the reaction media and catalyst. Thus, in parallel to the cellulose nanofibril production, concurrent lactic acid-catalyzed esterification of lactic acid to the cellulose nanofibers surface occured. The direct lactic acid esterification, which is a surface selective functionalization and reversible (de-attaching the ester groups by cleavage of the ester bonds), of the cellulose nanofibrils was confirmed by low numbers of degree of substitution, and FT-IR analyses. Thus, autocatalytic esterification and cellulose hydrolysis occurred without the need of metal based or a harsh mineral acid catalysts, which has disadvantages such as acid corrosiveness and high recovery cost of acid. Moreover, adding a mineral acid as a co-catalyst significantly decreased the yield of the nanocellulose. The lactic acid media is successfully recycled in multiple reaction cycles producing the corresponding nanocellulose fibers in high yields. The disclosed green cellulose nanofibril production route is industrial relevant and gives direct access to nanocellulose for use in variety of applications such as sustainable filaments, composites, packaging and strengthening of recycled fibers. 

A novel and sustainable tandem-catalysis system for asymmetric synthesis is disclosed, which is fabricated by bio-inspired self-assembly of artificial arthropod exoskeletons (AAEs) or artificial fungi cell walls (AFCWs) containing two different types of catalysts (enzyme and metal nanoparticles). The heterogeneous integrated enzyme/metal nanoparticle AAE/AFCW systems, which contain chitosan as the main structural component, co-catalyze dynamic kinetic resolution of primary amines via a tandem racemization/enantioselective amidation reaction process to give the corresponding amides in high yields and excellent ee. The heterogeneous AAE/AFCW systems display successful heterogeneous synergistic catalysis at the surfaces since they can catalyze multiple reaction cycles without metal leaching. The use of natural-based and biocompatible structural components makes the AAE/AFCW systems fully biodegradable and renewable, thus fulfilling important green chemistry requirements.

Herein, we describe efficient nanogold-catalyzed cycloisomerization reactions of alkynoic acids and allenynamides to enol lactones and dihydropyrroles, respectively (the latter via an Alder-ene reaction). The gold nanoparticles were immobilized on thiol-functionalized microcrystalline cellulose and characterized by electron microscopy (HAADF-STEM) and by XPS. The thiol-stabilized gold nanoparticles (Au-0) were obtained in the size range 1.5-6 nm at the cellulose surface. The robust and sustainable cellulose-supported gold nanocatalyst can be recycled for multiple cycles without losing activity.